BOATM Pulse Compressors

When ultrashort pulses propagate through material (even simple glass), they spread in time due to group-delay dispersion (GDD). The red colors propagate faster than blue colors, lengthening the pulse—we say that the resulting pulse becomes chirped—one of the reasons we need to measure it.

Swamp Optics' new single-prism (BOA--Bother-free Optimal Arrangement) pulse-compressor is an elegant device to re-compress your pulse.

Schematic of Swamp Optics' BOA single-prism pulse compressor

Why BOA?

We use a precisely manufactured corner-cube retro-reflector that reflects the beam back precisely parallel with the beam entering it. Also, it inverts the beam, so it isn't necessary to invert the prism. This avoids all the distortions of two- and four-prism designs (see the tutorial on pulse compression). Also, note that only the one prism angle needs to be rotated when the input wavelength is tuned, and only one distance (the prism-corner-cube distance) needs to be changed to tune the GDD. Even better, because the distance between the prism and corner cube is double-passed, the BOA compressor is half as large as an equivalent two-prism compressor. This simplicity yields a more compact, more convenient, non-distorting, and much less expensive device. And it works beautifully!

Yet another advantage of the BOA compressor is that, unlike all other pulse-compressors, it can be used with either broadband or narrowband pulses. The bandwidth of a prism pulse-compressor is limited by beam cropping of the angularly dispersed beam at the second prism (or at the second pass through the single prism in the case of the BOA). The greater the bandwidth of the pulse and the greater the prism separation (i.e., the required GDD), the more potential for such cropping. Conventional pulse-compressors tune the GDD by inserting one of the prisms into or out of the beam and always operate at their maximum prism separation. As a result, designing a conventional pulse-compressor requires committing to a pulse bandwidth and maximum negative GDD. Conventional narrowband compressors achieve large negative GDD, but cannot be used with broadband pulses. Conventional broadband compressors can be used for narrowband pulses, but they achieve only limited negative GDD. The BOA, on the other hand, tunes the GDD by translating the corner cube, thus varying the prism separation. This allows it to simultaneously operate at a large separation (GDD) for narrowband (<40 nm) pulses and also for broadband (>100 nm) pulses (which require less separation and GDD). Thus the BOA is much more versatile and can be used for many types of pulses. If you currently have a narrowband ~100fs system but are thinking of going to a broadband ~10fs system, you don't need to decide between two different compressors; one BOA will work for both systems! See below.

Award-winning design of BOA single-prism pulse compressor

Schematic of the conventional four-prism pulse-compressor.  Thick arrows indicate the alignments necessary to achieve proper operation. It's not a trivial matter to align one of these devices!

Operating range for the BOA compressor compared to conventional pulse-compressors.  Note that, unlike traditional pulse-compressors, which tune  the GDD by moving a prism into and out of the beam, the BOA can be used for both broadband and narrowband pulses. This is because it tunes the GDD by moving the corner cube, effectively changing the distance between the prisms of a multi-prism device--something that is impossible with a standard device.